Genetic Architecture of Glucosinolate Variation in Brassica napus

Glucosinolates (GSLs) are a group of secondary metabolites prevalent in the important oilseed rape crop (Brassica napus L.). The GSL hydrolysis products show diverse bioactivities and thus play significant biological and economical roles in the defence system and nutritional qualities of rapeseed protein meal. Hence, there is an increasing desire to harness the defensive properties of GSLs to improve pest resistance properties in the vegetative tissues while maintaining low GSLs in the seeds for animal feed.
This thesis aims to identify the genetic controls underlying natural GSL variations in the leaves and roots of B. napus, and also develop understanding of their connections with seed GSLs. To address these aims, Associative Transcriptomics (AT), was performed on a panel of 288 B. napus accessions. AT correlates GSL trait variations to the variations in either gene sequences or gene expression across these accessions to identify highly associated quantitative trait loci for GSL contents.
This thesis provides five key findings. Firstly, the GSL profiles differ extensively between the leaves and roots in both type and amount. Secondly, both the single nucleotide polymorphism and gene expression marker associations identify the MYB28/HAG1 orthologues on chromosomes A9 and C2 as key regulators for aliphatic GSLs in leaves. Thirdly, the reduced GSL levels in seeds reflect the reduced level of GSLs in leaves, and is due to the genetic variations caused by homoeologous exchanges in the genomic regions containing Bna.HAG1.A9 and Bna.HAG1.C2. Fourthly, AT and differential expression analyses of roots implicate Bna.HAG3.A3, an orthologue of MYB29/HAG3, as the main controlling factor for root aromatic GSL variations. Lastly, significant relationships exist between different classes of GSLs, suggesting some metabolic cross-talks between pathways. This work improves our understanding of the genetic regulatory of GSL natural variations in B. napus that could lead to crop improvement.